1. Field
The present disclosure relates to methods and devices for building large cylindrical tanks. More particularly, the present disclosure relates to a self-jacking scaffold for construction of large cylindrical tanks and to resist wind loads and other external loads.
2. Background Art
When constructing large storage tanks, the great height of the structure often requires that the tank be built in levels from the ground up. As these tank structures may be as tall as 40 m they are subject to wind loads. Conventional tank construction uses a large top stiffener and intermediate stiffeners to resist wind loads during construction. Typically, the top stiffener is also designed to serve as the scaffold at the top of the tank and provides access for construction. Top stiffeners, which also serve as the scaffold, are typically composed of plate girders.
Conventionally, scaffold systems may include a continuous scaffold that runs along a perimeter of the tank shell. Due to their great size, these structures are often assembled on the ground and attached to the tank shell in sections, each segment raised as the height of the tank increases. The top stiffener or scaffold is typically placed along the circumference of a tank shell. As construction continues and the scaffold must be raised to a greater height, the continuity of the top stiffener is broken to allow movement of the sections. As a result, the stiffener no longer provides the necessary stiffness for the shell to resist moderate wind loads.
This may pose a problem for large diameter tanks subjected to high wind loads, which require the top stiffener or scaffold to maintain the stiffness of the tank shell even as each section of the scaffold is raised. In order to minimize damage caused by wind loads the scaffold must be quickly detached, raised, and reattached to the tank shell. However, due to the size and weight of the scaffold sections as well as the accessibility of the connections between the sections, this process is often time consuming.